科研之友
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摘要
The temperature difference between the drilling fluid and formation will lead to an apparent temperature change around the borehole and tend to cause borehole instability problems in oil and gas drilling process. The wellbore stability models used in thinly laminated rock formations integrate the in situ stresses, pore pressure, well trajectory, and rock strength parameters to improve the wellbore stability; however, a limited amount of research has focused on the factor of formation temperature and its difference between drilling mud. Hence, a wellbore stability model is introduced based on the stress transformations and the Mohr-Coulomb failure criteria, which incorporate the rock strength anisotropy and the temperature difference between formation and drilling mud. The wellbore instability problems of anisotropic strength formation are analyzed using this model. The results show that the shear failure of rock matrix mainly occurs at two symmetric locations around the borehole and the size of failure region decreases with the inclination angle, in contrast, the shear slip failure of weak plane occurs at four locations around the borehole. The mud density required for isotropic strength should be selected as the required mud density to keep the wellbore stable if the inclination angle less than a certain value, and it almost keeps a constant with the inclination angle changes. On the contrary, the mud density required for slippage along the plane of weakness should be selected when the inclination angle larger than this value, and it is increasing with the inclination angle. Positive temperature difference will aggravate the wellbore instability, the larger the temperature difference the bigger the mud density is required.
- 出版日期2018-9
- 单位西南石油大学
